Collect. Czech. Chem. Commun.
1999, 64, 1641-1653
https://doi.org/10.1135/cccc19991641
Kinetics of Base-Catalysed Hydrolysis and Cyclisation of Substituted Acetamide and Benzamide O-(Phenoxycarbonyl)oximes
Jaromír Mindl*, Jaromír Kaválek, Helena Straková and Vojeslav Štěrba
Department of Organic Chemistry, Faculty of Chemical Technology, University of Pardubice, 532 10 Pardubice, Czech Republic
Abstract
The reaction kinetics of acetamide O-(4-nitrophenoxycarbonyl)oxime have been studied in aqueous buffers at pH 2-11. At pH > 9, the pH dependence of kobs is linear with slope 1, the cyclisation to 3-methyl-1,2,4-oxadiazol-5(4H)-one and 4-nitrophenol being the only reaction. At pH < 7.5, the only reaction is the hydrolysis giving 4-nitrophenol and acetamidoxime. The dependence of kobs on pH has been used to determine the rate equation and to propose the reaction mechanism. The cyclisation kinetics of substituted benzamide O-(phenoxycarbonyl)oximes have been studied in the pH range from 9.25 to 11. The reaction mechanism has been proposed based on the ρ constants found. In the first reaction step, the proton is split off from the NH2 group; the subsequent, rate-limiting step involves simultaneous N-C bond formation and C-O bond splitting.
Keywords: Reaction kinetics; Reaction mechanism; Oximes; Amides; Cyclisations; 1,2,4-Oxadiazol-5(4H)-ones.
